DE 10 2008 008 505 A1 discloses a combiner box comprising busbars to which the input connections for each string of photovoltaic modules are connected via disconnecting switches and a fusible link in one of the input connections. The busbars are connected to the output lines via a disconnecting switch. In order to be able to disconnect or connect the individual strings using a control unit, the disconnecting switches are connected in series with electronic switching elements between the input connections and the busbar. Furthermore, a current measuring unit for detecting a respective string current is connected in series with the respective electronic switching element. The control unit actuates the respective electronic switching element to disconnect the associated string if a respective detected string current measured value exceeds a prescribed comparison value. Typically, the comparison value is stipulated at a current value that is greater than 1.4 times the rated value of a photovoltaic module. Conventional fusible links are designed for higher values in order to prevent erroneous tripping of the fuse, e.g. as a result of aging, as a result of a temperature increase during operation and as a result of insolation peaks arising at a cloud speed of up to over 140% of the rated value. The advantages of the electronic fuses provided by the electronic switching elements in conjunction with the current measuring units and the control unit are their fast reaction to exceedances of the prescribed comparison value by the string current that arise and the fact that a tripped electronic fuse can be reconnected. The electronic switching elements arranged permanently in the flow of current from the individual strings to the busbars cause permanent power losses, however, and are a significant cost factor particularly when many strings are connected in parallel in a combiner box, particularly together with the fusible links that continue to be present.
US 2007/0107767 A1 discloses a further combiner box. In this case, busbars are connected directly to the output connections. Input connections for a respective string are connected to the busbars via a fusible link, a measuring device and a switching device. The measuring device measures a string current, and the switching device disconnects or connects the respective string. A control device evaluates the string currents and controls the switching devices. The control device can also be actuated by means of a remote control in order to operate the switching devices to connect or disconnect the strings. The switching devices may be actuatable switches or relays. A multiplicity of strings interconnected via the combiner box require many fusible links and relays to be provided in the combiner box, which signify a high overall cost involvement.
US 2006/0237058 A1 discloses a combiner box for which, in one input connection for each string, a fusible link is connected in series with a measuring device and a semiconductor switch. In the respective other input connection, a further measuring device is provided. The signals from the measuring devices are taken as a basis for ascertaining string currents, and these in turn are taken as a basis for actuating the semiconductor switches.
EP 2 282 388 A1 discloses an apparatus for supplying electric power from a multiplicity of strings of photovoltaic modules to a grid. In this case, multiple strings are respectively connected in parallel via a combiner box with protection by fusible links. For the output lines of each combiner box, an inverter has a separate connection provided on it, in which means for overcurrent protection and for selectively disconnecting the combiner box are provided. These means have a circuit breaker that can be opened and closed by motor. The circuit breaker is connected in series with a current measuring device in the connection. The means for overcurrent protection in the inverter have no fusible link.
WO 2007/048421 A2 discloses a switch fuse with control for solar cells. This is an electrical circuit arrangement for controlling the output of at least one of multiple strings, connected in parallel with one another using buslines, of photovoltaic modules. For the string, the circuit arrangement comprises a mechanical switch in order to interrupt one of the connecting lines of the string, a measuring device for measuring the current flowing through the string and a controller for receiving a signal from the measuring device and for controlling the mechanical switch. The controller is provided in order to open the mechanical switch if the current is not within prescribed limits.
WO 2013/081851 A1 discloses a combiner box having an input-side protection device that uses a protective switch or a fuse to automatically open the respective circuits affected by fault conditions, such as a ground fault or an overcurrent fault. All output connections of the protection apparatus are connected to a busline that can be connected to one of the output connections of the combiner box via a disconnecting apparatus.
US 2013/0050906 A1 discloses the practice of connecting multiple input and output lines to a central switch in the case of a safety device connected downstream of multiple combiner boxes as an alternative to a plurality of individual switches that can each be operated using a switch lever.